Oak Ridge National Laboratory (ORNL) announced last week that more than a dozen employees fell prey to a "a sophisticated cyber attack," exposing a database containing visitors' personal information.

In an advisory posted on Thursday, the federally funded lab recommended that people who have visited the lab between 1990 and 2004 place fraud alerts on the credit reports. The attack, which first breached a computer at the lab on October 29, 2007, did not gain access to classified information, ORNL maintained.

"A hacker illegally gained access to ORNL computers by sending staff e-mails that appeared to be official legitimate communications," the advisory stated. 'When the employees opened the attachment or accessed an embedded link, the hacker planted a program on the employees' computers that enabled the hacker to copy and retrieve information."

ORNL also stated that the attacks were "part of a coordinated attempt to gain access to computer networks at numerous laboratories and other institutions across the country."

Federal agencies and the national laboratory system have had to weather criticism over a number of compromises in the recent past. This year, congressional committees have grilled the Departments of State, Commerce, Homeland Security and Energy over data breaches. In May, the House Committee on Homeland Security sent questions to the Nuclear Regulatory Commission about a "data storm" that resulted in the emergency shutdown of a nuclear reactor at Browns Ferry plant.

The attack at Oak Ridge National Laboratory came from servers located in China, according to a memo obtained by the New York Times. Several nations have accused the Chinese military of sponsoring attacks on sensitive computer systems owned by governments and industry.